1. Field of the Invention
The present invention relates to a polygonal capacitor having terminals positioned with an improved precision.
2. Description of the Related Art
Capacitors for use in small electric apparatuses or electronic apparatuses include, for example, dip-type capacitors produced by directly coating a capacitor element with an insulating material and another type of capacitors having a capacitor element accommodated in a cylindrical or polygonal case formed of a metal or a resin.
A capacitor having a capacitor element accommodated in a case is easily attached to an electric or electronic apparatus through a hole formed in the case. Further, due to highly precise outer dimensions of the case, such a capacitor is easily and further automatically accommodated in the apparatus.
Whether a cylindrical case or a polygonal case is to be used is determined in consideration of the shape of the capacitor element, efficiency in usage of space and the like. More practically, a capacitor element produced by winding an insulating film having a metal evaporated thereof into a roll is generally accommodated in a cylindrical case. A capacitor element produced by laminating such insulating films or an oblong capacitor element having two linear sides and two arc sides is generally accommodated in a polygonal case.
An electrode of the capacitor element is connected to a terminal of the capacitor through a lead or directly.
For attaching such a capacitor to a precision component and especially for automatically performing such an attachment, positioning-precision with which the terminal is positioned with respect to the case is critical.
In the case of a capacitor element accommodated in a cylindrical case, the positioning precision is not very critical since the case is attached to the component while being rotated. A capacitor element accommodated in a polygonal case involves specific problems since it is required to determine the position of the terminal from a longitudinal side and a transverse side of the case.
FIG. 5 shows a conventional metallized film capacitor using a polygonal case.
A capacitor B includes a capacitor element 1 produced formed of a metallized film, a case 4 accommodating the capacitor element 1 and formed of a resin, and a resin 5 injected between the case 4 and the capacitor element 1. The capacitor element 1 has metal layers 2 formed on two side surfaces thereof to be connected to electrodes of the capacitor element 1. The metal layers 2 are formed of a metal by metallikon. The capacitor element 1 has terminals 3, which are welded to the metal layers 2, respectively, through base portions of the terminals 3.
The capacitor B is produced by putting capacitor element 1 having the terminals 3 into the case 4, injecting the resin 5 into the case 4 and then curing the resin 5.
In such a conventional capacitor B, it is difficult to put the capacitor element 1 so that the terminals 3 are precisely positioned as specified with respect to the case 4. Examples of the reasons for the difficulty are: (1) the positional connection between the terminals 3 and the capacitor element 1 is not sufficiently accurate; and (2) the terminals 3 are positionally displaced with respect to the case 4 when the capacitor element 1 is put into the case 4. Further, care should be taken to prevent the capacitor element 1 from moving in the case 4 when the resin 5 is injected into the case 4, in order to maintain the positional precision of the terminals 3 with respect to the case 4.
FIGS. 6 through 8 show another conventional capacitor. In this capacitor, grooves 6 are formed at inner surfaces of the case 4, and an end portion of each terminal 3 is inserted into the groove 6. Such a construction can prevent the movement of the terminals 3 in an X direction (FIG. 7) along the inner surfaces of the case 4, but cannot prevent the terminal 3 from slanting in a Y direction as is shown in FIG. 9 or from moving in a Z direction as is shown in FIG. 10.